n=1. I wear my shoes until the soles start to wear thin. Usually get 500 miles.
Only injury in the last 10 years was a twisted ankle when running a rooted trail.

I have no idea whether a study has been done. What I do know is that when I switch out my shoes at ~300(ish) miles, there's a noticeable difference in the cushioning of the new shoes. Being 50 years old, and having had my share of running injuries, I'll just chalk this one up to "cheap insurance" and keep swapping them out every 300ish miles.

Another n=1. I don't know of any studies.

I used to be very injury prone running. And, I was VERY sensitive to shoe age, never getting more than about 300-320 miles out of a pair. Any time I pressed past that point by any significant amount I would get niggles of one kind or another.

After a long stretch (many, many months) of heavy PT, I no longer seem to be susceptible (well no more than anyone else). My last pair of shoes I ran up to 483 before I retired them, which was just because they weren't providing any cushioning any more. I have a few gravel roads on my normal rotations, and I could feel the rocks and stuff on the road surfaces. They were starting to bruise the soles of my feet. If I were on exclusively smooth surfaces, I probably could have gone another 100mi.

So, maybe all that is to say that the better your mechanics...and less injury prone, the less shoe mileage matters. But, for someone like the "old me", shoe mileage matters a great deal.

300 is a rule of thumb.

Back in the day (80's) the sheet EVA foam used for most shoes (ex. the Jazz below) would compress significantly by that point, leaving shoes with less cushioning and a notable slant. Nike Air was originally designed to help address the compression issue.


Today's shoes have vastly improved midsole materials that go much longer before taking on a significant compression set. I have a pair of Adidas Boost shoes and I'm pretty sure the midsole will be the last part of the shoe to fail. There is a lot of variation though. Some of the EVAs are much improved, but not as long lasting as other options.

Taking all that into account, there is still the additional variability from a number of factors (that's why 300 is just a rule of thumb....and an outdated one at that).


Runner weight (a runner wearing a 9.5 shoe might weigh 135, or 235)

Footstrike (heel vs midfoot vs forefoot)

Running surface (you'll get a lot more mileage running on pine needle trails or an all weather track than chip&seal)

Shoe type (a racing flat won't last nearly as long as a bulky trainer [duh]...lightweight trainers like Kinvaras are in the middle) (I used to have some aptly named Nike Mayfly flats that were designed for a lifespan of 62miles)


Personally, if you can't get 500+ miles out of your daily trainers something is probably off.

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ECMGN Therapy Silicon Valley:
Depression, Neurocognitive problems, Dementias (Testing and Evaluation), Trauma and PTSD, Traumatic Brain Injury (TBI)

I would say its definitely mostly a marketing ploy to get you to buy new shoes... although I definitely notice reduced cushioning as you start to approach 300-400 miles. I typically track when I switch to new shoes, but would never use that to decide when to switch. I simply switch when the reduced cushioning starts to cause foot discomfort during my runs.

In my experience once I get over 300sh miles per pair I get all sorts of aches and pains. Those go away within a few days of switching to a fresh pair of shoes.

Soooo.....NOT marketing. But, maybe not a hard and fast rule at EXACTLY 300 miles.

Outside soles were wearing out, I ran with them anyway and I could feel discomfort on my knees and ankles around 6-7 miles into it. I ditched them and got a new pair. When I was landing, angles were slightly off and that caused it. When I’m fresh, I don’t feel that much but if I go out for a long run, I can definitely feel it. I don’t know how many miles are on mine but you can tell bottom soles are not even.

I run until they feel flat then I switch and notice a big difference in cushion. I would guess around 400-600 miles.

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http://www.sfuelsgolonger.com

I'd take a slightly different tack on this. We seem to be saying that the loss of cushioning accelerates. They are fine for hundreds of miles then they aren't. Maybe this has come from marketing or general running wisdom but I'm not sure it makes much sense. Wouldn't it be more logical if the loss of cushioning decelerated? If we were talking about a hard metal part then sudden drop off would make sense as it fails but for a shoes mid-sole I don't see that happening.

If I started smacking some foam with a hammer wouldn't I notice big changes at the start and then then less as the foam was compacted and there was gradually less and less opportunity for that foam to keep compressing?

So wouldn't the biggest loss of cushioning be at the start of a shoes life and then that loss would gradually slow down? To me that actually makes anecdotal sense because new shoes seem different but it doesn't last long. For me shoes don't suddenly drop off a cliff and become suddenly flat. It's more they are unhygienic or some part of the shoe fails like the sole wears through of the upper splits. But cushioning wise they have just been ok for a while.

If a shoes cushioning loss was accelerating then wouldn't the cutoff point be pretty dramatic? It would be getting worse faster. It would curve down until it hit zero then have nowhere to go. That point would be glaringly obvious and you might as well be running barefoot on concrete. On the over hand if it was decelerating there would probably be a minimum cushioning it would approach but never actually reach. I haven't fully thought this through but that seems to better match my experience

No offense, but I think you're perhaps overthinking it a bit ;-)

Regardless of what the "foam cushioning degradation profile" is (lose more early then rate of decay decreases, or vice versa, or linear, or... or...) I think everyone agrees that at some point the shoes have lost enough cushioning that retiring them is warranted. When, exactly, that point is likely varies by shoe, shoe size, weight of runner, running surface, and a million other factors. I don't feel like going all CSI on my running shoes, so I switch them out every 300 miles and I can feel the difference. That's good enough for me. I got better things to occupy my brain cells with. In the grand scheme of all things triathlon-related, that's a pretty minor expense.